Generation and growth of aerosols over Pune, India

The measured physical size distributions of sub-micron particles during cold season at Pune, India are analyzed to explore the characteristics of nucleation and growth properties. Preliminary analysis of aerosol size distribution in time-series shows large increase in number concentration due to nucleation events between 0800 h and 1030 h at this location. The observable quantities such as condensable vapor concentration (C), its source rate (Q), growth rate (GR) and condensable sink (CS) are estimated from the time-series evolutions of aerosol size distributions. The concentration of vapor and its source rate were about 19.8 ± 2.15 × 107 molecules cm−3 and 1.28 ± 0.084 × 107 cm−3 s−1 respectively. The average condensation sink and growth rate were 7.1 ± 0.4 × 10−2 s−1 and 16.95 ± 1.86 nm h−1 respectively during the growth period. The values are high enough to trigger the nucleation bursts and enhance subsequent growth rates of nucleation mode particles at this location. The magnitudes are in the range of those observed at New Delhi, India and much higher than those of European cities. The ratio of apparent to real nucleation rate is found to be a measure of number concentration of freshly produced particles by photo-chemical nucleation. The predicted number concentrations corresponding to measured distributions of mid-point diameter increases with the size for both 1 nm nucleated clusters and 3 nm particles. The database of all the possible event days and the event characteristics forms the basis for future works into the causes and implications of atmospheric particle formation at this location.